1. Field of the Invention
This disclosure generally relates to the field of automatic data collection (ADC), and more particularly to machine-readable symbol readers for reading machine-readable symbols, for example bar code symbols, area or matrix code symbols, and/or stack code symbols.
2. Description of the Related Art
A variety of machine-readable symbol readers for reading machine-readable symbols are known. Such readers typically employ one of two fundamental approaches, scanning or imaging.
In scanning, a focused beam of light is scanned across the machine-readable symbol, and modulated light returned from the machine-readable symbol is received by the reader and demodulated. With some scanning-type machine-readable symbol readers, the machine-readable symbol is moved past the reader. With others, the reader is moved past the machine-readable symbol. More commonly, the reader moves a beam of light across the machine-readable symbol, while the reader and machine-readable symbol remain approximately fixed with respect to one another. Demodulation typically includes an analog-to-digital conversion and a decoding of the resulting digital signal.
Typically, scanning-type machine-readable symbol readers employ a light source that produces a scanning beam that may not be visible in the human range of visual perception. For example, the machine-readable symbol reader may employ a source such as a laser diode, which emits electromagnetic radiation in the infrared range. Even where the light source is in the visible range, the scanning beam is often difficult or impossible to see, for example in bright light conditions and/or at long read ranges. This makes it difficult for the user to properly aim the machine-readable symbol reader at a desired target. It is particularly difficult where targets are closely spaced, for example where carried on items stacked on a pallet or in a warehouse.
Previous attempts to solve this problem have included using a brighter scanning beam. A brighter scanning beam, however, has a number of disadvantages, including high power consumption and limits placed on the power of lasers by various administrative agencies such as the Occupational Safety and Health Administration (OSHA). Another approach has been to provide a separate light source that emits a highly visible beam of light, commonly referred to as a pointer beam. This approach typically includes the use of a multi-function trigger, allowing a user to illuminate a target with the pointer beam, and then turning the pointer beam OFF and turning the scanning beam ON. This prevents the pointer beam from interfering with the reception of the scanning beam reflected or backscattered by the machine-readable symbol. Again, this approach has a number of disadvantages including high power consumption, and may lead to inaccurate scanning since the pointer beam and scanning beam are not on at the same time.
There is a need for a low-cost machine-readable symbol reader with an aiming mechanism that ensures reliable aiming. There is also a need for a low-cost machine-readable symbol reader that does not require a multi-position or multi-function trigger. There is a further need for a low-cost solid state machine-readable symbol reader. Further, there is a need for a low-cost machine-readable symbol reader where the pointer beam and the scanning beam are on at the same time to allow accurate aiming and scanning.